Mixed flow augmentation system

ABSTRACT

1. In an axial flow reaction engine a mixed flow augmentation system comprising: A FIRST PLURALITY OF MOTIVE FLUID FLOW PASSAGES; A SECOND PLURALITY OF MOTIVE FLUID FLOW PASSAGES, THE PASSAGES OF SAID FIRST AND SECOND PLURALITIES HAVING OPENINGS INTERSPERSED IN CIRCUMFERENTIAL ALTERNATION ABOUT THE AXIS OF THE ENGINE; AND A PLURALITY OF RADIALLY-EXTENDING FLOW BLOCKAGE MEMBERS LOCATED ENTIRELY WITHIN THE FLOW PASSAGES OF SAID SECOND PLURALITY UPSTREAM OF THE OPENINGS THEREOF, WHEREIN THE PLANE OF MAXIMUM AERODYNAMIC FLOW BLOCKAGE OF SAID MEMBERS IS CO-PLANAR WITH THE PLANE OF STATIC PRESSURE BALANCING BETWEEN THE MOTIVE FLUID STREAMS OF SAID FIRST AND SECOND PLURALITIES OF FLOW PASSAGES, RESPECTIVELY, TO FACILITATE FLOW MIXING AND COMBUSTION STABILITY IN SAID MIXED FLOW AUGMENTATION SYSTEM.

United States Patent 11 1 Vdoviak et al.

[ MIXED FLOW AUGMENTATION SYSTEM 1 Aug. 7, 1973 Primary ExaminerSamuelFeinberg 75 Inventors: ohn vdovi I Attorney-Thomas J. Bird, Jr., Lee H.Sachs, Oscar B. 1 i weinstei: 'gfi gg t gg Waddell, Frank L. Neuhauser,Derek P. Lawrence and Ohio 1 Joseph B. Forman [73] Assignee: GeneralElectric Company, EXEMPLARY CLAIM Cincinnati, Ohio I. In an axial flowreaction engine a mixed flow aug- [22] Filed: Aug. 7, 1963 mentationsystem comprising: [21] Appl, N13,: 300,432 a first plurality of motivefluid flow passages;

' a second plurality of motive fluid flow passages, the 52 us. Cl.60/261, 60/262 Passages Said first and sewn! Plural"ies having 51 Int.Cl. "1. 02s 3/10 Penings interspersed circumferential alematim 58 Fieldof Search 60/35.6, 261, 262 the engine; and

a plurality of radially-extending flow blockage [56] References Citedmembers located entirely within the flow passages of U TE STATES PATENTSsaid second plurality upstream of the openings thereof,. 2 929 203311960 Banning Jr at 60/35 6 wherein the plane of maximum aerodynamicflow 2 934:895 5/1960 Gregory et 51. ...II"""'IIIII1 60/35I6 bhckagesaid members is with Plme 975,589 3/1961 Vdoviar 60 356 of StaticPressure balancing between the motive fluid 2,978,865 4/1961 Pierce 0 355 streams of said first and second pluralities of flow 2,979,900 3/1961Hopper 60/35.6 passages, respectively, to facilitate flow mixing and3,043,10! 7/1962 Lefebrre et al. 60/35.6 combustion stability in saidmixed flow augmentation 3,048,376 8/1962 Howald et al 60/35.6 system 10Claims, 11 Drawing Figures I I Z 4a, K y H UH "11:1 ll "(3 4 rd! 2 4.

PATENTEW' 3. 750.402

sum 3 or 4 Z? I i 5 INVENTOR Y 1 H B Ja/m m rear/4w MIXED FLOWAUGMENTATION SYSTEM The present invention relates to a thrustaugmentation system for a reaction engine and, in particular, to a mixedflow augmentation system for a turbofan engine.

A well known type of prime mover for propelling vehicles, suchasaircraft, is an engine wherein a stream of hot exhaust gases issuingfrom the rear of the engine propels the vehicle by reaction of the hotgas stream, or jet7 upon the vehicle through the engine fixed therein. Acommon form of jet engine is an axial flow gas turbine known as aturbojet" wherein air is compressed in a rotating compressor, mixed in acombustion chamber with fuel and the fluid mass expanded by burning. Thehot motive fluid from the combustion chamber flowsaxially through apower turbine mounted on the same shaft as the compressor to cause ittorotate, the hot exhaust gases thereafter passing out through theengine tailpipe to provide the propulsive jet. In a turbojet no excesspower (other than that required to drive the compressor) is supplied bythe turbine.

Another form of gas turbine jet engine is the turbofan, sometimes calleda by-pass" engine. Examples of this type of engine are shown in thePatents to Whittle No. 2,405,919 and Godsey No. 2,404,954. Such enginesusually comprise a cylindrical duct or casing spaced concentricallyabout a conventional turbojet engine to provide an annular by-pass gaspassage. The inlet to the inner gas generator (turbojet) is typicallylocated downstream of the outer duct inlet and provision may be made forat least the early stages of the compressor to extend across both ducts.This forward portion of the compressor, sometimes called the fan,provides increased engine mass airflow, without an appreciable increasein engine weight or fuel flow, and, thus, is a form of thrustaugmentation. The cold" and "hot",streams emerging from the fan orby-pass duct and the inner gas generator duct, respectively, may bemerged somewhere upstream of the outlet of the turbofan engine beforeexiting as a mixed flow stream.

It is also customary in jet engines for use in aircraft design to fly attransonic and supersonic speeds to provide an additional means of thrustaugmentation sometimes termed reheat. Thus, it is known that'after thehot fuel/air mixture has passed through the main gas generator cycle,there remains some additional thrust potential since not all theavailable oxygen has been consumed. Therefore, with the addition of morefuel and provision of means for igniting the enriched fuelair mixture inthe engine tailpipe, additional .thrust may be realized. However, in theby-passor turbofan engine mixed flow augmentation presents certainproblems for the engine designer. For example, the presence of dual highvelocity concentric flow streams makes it difficult to ensure sufficientcombustion of both streams, with low pressure loss, as well as providingefficient mixing and combustion stability, along with optimum flowmatching and pressure equalization. While other flow mixing principleshave also been applied to by-pass or turbofan exhaust mixing, such asaxially-extending, elongated, perforated duct means separating thestreams, it is known that by-pass engine augmentation may be enhanced bythe use of the so-called 'daisy chute" mixing principle. An example of atype of "daisy chute" mixer is shown in the Patent to Lloyd No.2,426,833 wherein a circular member, having inner walls deeplycorrugated, i.e., star-like in crosssection, provides alternating fluidstreams in an interdigited relationship flowing through and out of themember. Use of a daisy chute type mixer can, however, create seriousproblems of added weight and gas pressure losses when inserted in theexhaust stream such that the use thereof would be prohibitive from anengine performance standpoint. Thus, unless particular attention is paidto the aero-thermodynamic design of a daisy chute mixer in a flowaugmentation system to ensure, for example, that the length and weightof the device is held to a minimum, undue pressure loss penalties or lowcombustion efficiency can result. The design problem can be furthercomplicated where it is desirable to provide a mixed flow augmentationsystem wherein the thrust level must be continuously modulated from alow temperature rise initial light-off of the augmentation system toprevent fan "stall" to maximum reheat with smooth operation, i.e., nosudden thrust jump" which can result in damage to the engine oraircraft, if severe.

it is, therefore, a general object of the present invention to providean improved mixed flow thrust augmentation system for use with aturbofan or by-pass type gas turbine engine.

A more specific object of the invention is to provide a mixed flowthrust augmentation system utilizing an improved daisy chute type mixerof short, compact and lightweight design providing lower gas streaminsertion (pressure) losses.

Another object of the subject invention is to provide a mixed flowaugmentation system for a turbofan engine utilizing a daisy chute mixerhaving an improved hot gas flow blockage or flameholding arrangement toensure optimum flow diffusion ratios to increase system efficiency.

Still another object of the subject invention is to provide a mixed flowaugmentation system utilizing a daisy chute mixer wherein staticpressure balancing or matching of the by-pass and gas generator streamsat the mixer exit is controlled for greater combustion stability,efficiency, and lower overall system pressure losses.

A further object of the invention is to provide a thrust augmentationsystem utilizing a daisy chute mixer having improved flow matching andflow equalization characteristics, in addition to improved mechanicalreliability, in combination with a staged fuel injection systemproviding smooth, wide fuel flow (thrust) modulation from light-off ofthe augmentor to maximum reheat operation.

Briefly stated, one embodiment of our invention comprises thrustaugmentation means for a turbofan engine having a by-pass duct and a gasgenerator spaced within the by-pass duct including a first plurality ofcontoured diffusion passages in flow communication with the by-passduct, a second plurality of contoured diffusion passages in flowcommunication with the gas generator, the passages of the first andsecond pluralities being interspersed in circumferential alternationabout the axis of the engine with the passage walls common to both ofthe pluralities being configured so that (l) upstream of a plane ofcontour the flow area of each passage of both plurallties is continuallyincreasing in a downstream direction, (2) downstream of the plane ofcontour the nominal flow area of each passage of the second plurality isincreasing at a greater rate per unit length than upstream of the plane,and (3) the flow area of each passage of the first pluralitysubstantially decreases downstream of the plane in direct proportion tothe nominal flow area change of the passages of the second pluralitydownstream of the plane. A plurality of radial flameholders are locatedwithin the passages of the second plurality so that the plane of maximumaerodynamic flow blockage is co-planar with the plane of static pressurebalancing between the by-pass and gas generator streams. An additionalcircumferential flameholder provides cross-firing of the radialflameholders. Also provided are sequentially additive staged fuelinjection means for injecting fuel locally of the circumferentialflameholder member for initial augmentation, locally of the radialflameholders for intermediate power requirements, and uniformlysubstantially upstream of the plane of the radial flameholders formaximum power.

The features of our invention which we believe to be novel are set forthwith particularity in the appended claims. The invention itself,however, both as to its organization and method of operation, togetherwith further objects and advantages thereof, may be best understood byreference to the following detailed description and the accompanyingdrawings in which:

FIG. I is an axial cross-section view of a by-pass or turbofan jetengine utilizing the subject invention;

FIG. 2 is a partial perspective of the embodiment of the mixed flowthrust augmentation and staged fuel injection means shown in FIG. 1;

FIG. 3 is a view taken along the line 3-3 of FIG. 1;

FIGS. 4a, 4b, and 4c are enlarged cross-sectional, partial views of themixed flow augmentation means of the subject invention in schematic formtogether with known prior art devices included for comparison purposes;

FIGS. 5a and 5b are partial schematic plan views of the adjacent by-passand hot gas generator passages of the improved daisy chute mixer of thesubject invention illustrating the particular contouring of the commonpassage walls thereof and the location of the radial flameholder meanswith respect to the plane of contour;

FIG. 6 is a graph illustrating the flow area variation in the passagesof the daisy mixer embodiment of FIG. 1, and further illustrating theeffect of locating the radial flameholder as shown also in FIGS. 5a and5b;

FIG. 7 is a schematic view of the location of the staged fuel injectionmeans of the subject invention in another embodiment thereof; and

FIG. 8 is a graph illustrating total fuel flow in units per time in theaugmentation system of the invention and indicating various combinationsof the sequentially additive system, shown in FIGS. 1, 2 and 7;

Turning now more specifically to the drawings, shown in FIG. I is across-sectional view of an axial flow gas turbine engine of the by-passor turbofan type, although it will be understood that the inventioncould find equal utility in other types of reaction or jet engineshaving requirements for mixing dual flow streams of motive fluid. Thus,the engine comprises an outer or by-pass duct indicated generally at I,having a forward inlet opening area 2 and an outlet or engine tailpipeexhaust area at 3. Within the outer or by-pass duct of this axial flowjet engine and located just aft of the inlet area 2 is a forward or lowpressure compressor 4. It will be noted that the forward compressorextends across the outer duct inlet area and thus will act to raise thepressure, and temperature, of all the air entering the engine. Theforward compressor is mounted on a shaft 5 which is supported onbearings indicated at 60, 6b and 6c. Located at the rear, i.e.,downstream, of the forward compressor is an inner gas generator duct 7which in combination with the spaced concentric duct 1 forms a by-passflow passage 8 for the forward compressor or fan" air. Part of thecompressed air from the forward compressor or fan enters the inlet area9 of the gas generator duct where it is further compressed by the gasgenerator compressor 10. The highly compressed air then enters thecombustion chamber area indicated at I] where it is burned with fuelinjected through suitable main fuel injection means 12. The hot gaseousmixture thereafter passes through the power turbine 13 also mounted onshaft 5. Work to power the rotating compressors is removed from thestream by the power turbine, which may comprise three stages or wheels,as shown, although more or less than the three described could beutilized depending on the engine requirements. The hot gas generatorgases exit from the power turbine passing around the faired strut orframe members 15 which support the bearings 6c. These struts are part ofthe turbine rear frame structure which extends across both the by-passduct and the hot gas generator stream and, thus, the struts will have anaerodynamic shape. Other strut or frame members 16 and 17 are located inthe area of the bearings 6b, 6a respectively, to help supporttherotating members and the inner gas generator duct in a known manner.The exhaust discharge or exit 3 is typically made variable in area bysuitable nozzle means indicated generally at 18. It may be desirablealso to provide an annular or plug type nozzle having an inner, bulbousmember indicated at 19. The plug member may be supported by a long shaftor extension 20 mounted to the turbine rear frame. Indicated generallyat 21 is a diffuser section, wherein the exhaust gas velocity isdecreased in both air streams simultaneously with a concommitant rise instatic pressure and wherein the novel mixed flow thrust augmentationsystem of the subject invention, now to be described, is located.

Turning now to FIG. 2, which is an enlarged partial perspective view ofthe mixed flow augmentor system, the large solid arrows illustrate theflow path of the hot gas generator stream. The large cross-hatchedarrows, on the other hand, indicate the flow path from the cold by-passpassage. Reference to FIG. 3, as well as FIG. 2, will make it clear thatthe hot and cold streams are thus interspersed in circumferentialalternation around the axis of the jet engine. The hot gas generator andthe cold by-pass flow passages are formed by a convoluting, continuouswall member, indicated generally at 22, having a common passage wall 24between adjacent hot and cold streams joined by generally laterallyextending wall portions 25 at the outer periphery of the member 22 andsimilar wall portions 26 at the inner periphery thereof. Thisconfiguration provides a series of alternating cold and hot lobes orpassages 27 or 28, respectively, somewhat akin to the so-called daisychute mixer described above. Thus, it will be seen that the bypass airenters the passages 27 through an upstream inlet 29 in communicationwith the by-pass duct 8. On the other hand, flow from the hot gasgenerator stream enters the mixer 22 at the open upstream area 32, withboth the hot and cold streams exiting over the mixer lip or edge 35 atits downstream end. The described embodiment also provides an outerannulus of cooling air flow over the outer lateral wall 25, as indicatedby the small cross-hatched arrows. This airflow serves to cool both thelaterally extending wall which contains the combustion gases and theadjacent diffuser casing section. inwardly of the laterally extendingwall portions 26 at the inner periphery of the member 22 there isprovided an annular hot stream indicated by the small solid arrows. Thisis useful for initial low thrust augmentation, as hereinafter described.

To obtain desired reheat or thrust augmentation, means must be providedfor injecting additional fuel into the motive fluid downstream of themain gas generator and igniting same. One embodiment of our inventionincludes a three stage fuel injection system.

The system includes a plurality of radially-extending flow blockagemeans or flameholders indicated generally at 40 located completelywithin the hot gas generator flow passages 28. The radial flameholders40 are in communication with a circumferential or annular flameholdermeans indicated at 42 located in the inner annular hot gas streamdepicted by the small solid arrows for purposes of cross ignition. Theflameholders or flow blockage means 40 and 42 typically comprisediverging substantially flat wall portions 44 and 46 meeting at anupstream apex 47 to provide a recirculation zone, generally indicated at48, substantially encompassed by the diverging wall portions. Thestagedfuel injection system shown in the drawings also includes a first fuelinjection means 50 located just upstream of the apex of the flameholderand extending radially inward to inject fuel locally, (i.e., immediatelyupstream of the apex) of the circumferential or annular flameholder 42.A second fuel injection means 32 is shown extending generally parallelto the first fuel injection means and on the inside (downstream of theapex) of the radial flameholder means 40. Fuel injected from the secondfuel injection means therefore deter- Note that the annular flameholder42 is operable to cross-fire the radial flameholders. Further, the coldstream width is substantially equal to that of the hot streams, whichwill facilitate better mixing and, hence, improve performance at higherby-pass ratios (i.e., the ratio of the cold air mass flow to the gasgenerator fluid mass flow in the turbofan).

Certain of the advantages over known devices presented by our inventionin the areas of combustion stability in a turbofan reheat system,reduction of weight and complexity of the mixer device, and greatercontrol over the gas generator stream diffusion ratio; are perhaps mademore significant in the schematic drawings and graphs of FIGS. 4 and 6.As stated above, an object of our invention is to provide a mixed flowaugmentation system utilizing an improved daisy chute type mixer ofcompact design to reduce pressure (insertion) losses over known designs,for example, by an arrangement which permits a decrease in the length ofthe mixer. FIGS. 4a-4c indicate areas of improvement by the contrastbetween the arrangement of the present invention FIG. 4a and certainarrangements commines the fuel/air ratio in the recirculation zone 48 ofthe radial flameholder. The first fuel injection means could be locatedotherwise than as shown but in the position depicted, i.e., just forwardof the radial flameholders, the blockage of the hot gas generator streamissubstantially unaffected. This arrangement also simplifies connectionof the first and second fuel injection means to annular fuel manifolds53 and $4, respectively, placed around the duct or casing 1 in zone 21.Located adjacent the aforementioned fuel manifolds is a thirdmanifoid 55which supplies fuel to the third fuel injection means 56 of the threestaged fuel injection system of the invention. The third fuel injectionmeans is located substantially upstream of the radial and annularflameholder means, that is, at the entrance of the mixer member 22. Thisarrangement enables fuel injection to be uniformly distributed in thehot gas generator duct for higher engine power requirements, ashereinafter more fully explained. Finally, ignition means in the form ofan igniter or spark plug, indicated in dotted lines at 60, is suppliedto initiate light-off of the combustion fluid in the thrust augmentonlnthe arrangement shown in FIG. i, wherein an annular plug nozzle is used,the plug nozzle support member 2t) may be shielded by an annular memberas from the effects of the hot gas stream.

FIG. 3 is included to indicate the relative placement and lateralarrangement of the hot and cold streams.

bining one or more known devices, as illustrated in FIGS. 4b and 4c.Specifically, the drawings illustrate the particular placement of theradially-extending flameholders 60 with respect to the end or lip 35 ofthe mixer member 22. It is known to be advantageous to place flamestabilizing means in the hot gas stream only of a dual flow (by-pass andhot gas generator) mixing device to achieve a low pressure (insertion)loss, stable combustion (particularly at low operating pressures) andefficient control at the lower power requirements, since the amount offlameholder stream blockage needed for stabilization is inverselyproportional to inlet temperature and directly proportional to pressuredrop, that is, smaller and less weighty members can be utilized whenthey are placed in the high temperature stream. Further, as statedabove, daisy chute type mixers can provide relatively high efficiencymixing in a relatively short length. Nevertheless, the known prior artdevices suffer from certain disadvantages. For example, the arrangementof FIG. 4b does not segregate the by-pass and gas generator flows up tothe mixer exit, as does our arrangement, as shown in FIG. 40. Thus, theknown device permits premature dilution of the hot and cold streamsprior to fuel injection, which adversely affects combustion stability.This is not allowed in the present invention. Furthermore, placing theflameholder means within the mixer, as in FIG. 4a,

provides more efficient flow distribution over the entire radial heightof the mixer, which is not possible with the designs of FIGS. 4!) anddo.

More importantly, however, the arrangement of our invention permits fanand gas generator stream static pressure balancing at the maximumaerodynamic width of the flame blockage. This is slightly aft of thephysical maximum width of the flameholder, that is, just downstream ofthe mixer exit. This provides a much more well defined matching planethan heretofore has been possible. Improved flow matching, that is,static pressure balancing of the two streams (where static pressurerefers to the pressure within the stream other than that provided to itby the velocity component of the molecules thereof), minimizes backpressure, in particular, on the fan or by-pass stream. This in turnenhances mixing efficiency and efficient operation or control of theoperating limits of the fan or forward compressor. This is made possiblewith our invention since flow matching will occur with the arrangementof FIG. 4a prior to encountering heat addition losses in the gas streamsdue to combustion. That is, little, if any, effective combustion willoccur in the hot gas stream prior to the flow reaching the exit plane ofthe mixer and in the area of maximum aerodynamic flow blockage. Inaddition, it will be noted that the known arrangement of HG. 4b presentsan obvious attendant disadvantage of increased weight pressure losses byreason of the spacing of the mixer from the inner duct to accommodatethe annular upstream mixing gap. More importantly, however, theconventional arrangement of FIG. 4 b suffers from the requirement thatstatic pressure be balanced at two locations, i.e., at the annular gapand at the mixer exit. As pointed out hereinabove, at different flightspeeds by-pass and gas generator flow conditions will vary. For example,at higher flight Mach numbers, the by-pass ratio will be higher than atlower speeds. Thus, matching at two locations would require flowshifting at the mixer inlet and acceptance of greater losses, since flowshifting will cause separation losses.

On the other hand, the arrangement of FIG. 40 illustrates means wherebystatic pressure balancing of the by-pass and gas generator streamsoccurs at or immediately downstream of the mixer exit. This, however,has also shown to be undesirable since there ideally should be nodilution of the hot stream at the flameholder or flow blocking region orcombustion inefficiency will result. More specifically, the gasesexiting from the mixing device will be in a turning flow field due tothe direction given by the diasy chute mixer walls and due to theblockage effect of the flow stabilizing means. Establishing the desiredstatic pressure balance for such a flow system is difficult if notimpossible, particularly under changing flight conditions. To achievesome measure of control, therefore, it has been customary to move theflameholders aft (see solid line position in FIG. 4c). However, thisrequires additional length of the diffuser and mixer, since additionalgas generator flow area will be required to achieve the necessary staticpressure balance, with a resultant larger total flow area at thematching or static pressure balancing plane. If, on the other hand, theflame stabilizing devices are moved considerably downstream of themixer, they will be located in an area where the streams aresubstantially intermixed. Little or no control over augmentationstability is possible at this point, however, due to the fact thatintermixing is usually accompanied by some turbulence unless, of course,the mixing duct is extremely long in length. Even in the lattersituation, where the cold and hot flows may possibly stratify over theflow area of the exhaust duct, to attempt to place the stabilizing meanswithin certain strata, particularly where the engine must operate underdifferent flight conditions and with changing bypass ratios, is verydifficult. Thus, our invention situates the maximum aerodynamic flowblockage area not only upstream of the mixing area but co-planar withthe plane of static pressure balancing, which, with the configurationdisclosed herein, may be controlled extremely well as to location.

FlGS. 5a, 5b and 6 are included to emphasize the unique contouring ofthe hot and cold flow passages in the improved mixer 22 of our thrustaugmentation system. it will be noted that starting at a "plane ofcontour", the common passage walls 24 are contoured around theflameholders 40 to obtain maximum diffusing rates, i.e., shorterdiffuser length in the mixer. Thus, the radial flameholders are locateddownstream of the plane of contour and in the area of shared diffusion,i.e., in the flow passage area where the common wall 24 diverges orenlarges the nominal flow area of the hot stream passage 28 about theflameholder, at the same time decreasing, or converging, the flow areaof the cold air or fan passageway 27. An additional benefit of ourarrangement, therefore, is reduction of the flow area expansionrequirement for the gas generator stream since the gas generator streamtotal (nominal) area is increased rapidly about the flameholders. Thisarrangement also provides aerodynamic acceleration of the gas generatorstream and, further, reduces the overall mixer diffusion ratio.

It is known that control of the velocity of the gas flow in the area ofthe flameholder or stabilizing member can result in improved combustionstability. Contrary to known arrangements, however, whereby the staticpressure balancing between the by-pass and gas generator streams occursahead of the flameholder (although the flameholder itself may beupstream of where the hot and cold stream start to mix, e.g., FIG. 40),control of flow velocity past the flameholder is more easily obtainedwith our invention. In other words, it can be shown that flow velocityover the flameholder will depend on how well the static pressure balancehas been accomplished. Thus, the known prior art devices suffer fromless direct control over the flameholder lip velocity since in the knownarrangements the lip velocity is made completely dependent on staticpressure balancing. As pointed out, with changing flight demands, therewill be less control over combustion stability, i.e., less efficient useof the reheat fuel for thrust augmentation. it should therefore be clearthat with the maximum flameholder wake diameter positioned as shown inFIG. 5, that is, right at the mixer exit plane as s result of placementof the flameholders as shown in FIGS. 1, 2 and So, there is provided amuch more efficient thrust augmentation system than has heretofore beenpossible.

FIG. 6 further illustrates the design of our improved mixer.Specifically, the graph shows that the nominal flow area of the hot gasgenerator passage 28 is increasing upstream as well as downstream of theplane ofcontour (although effectively the area increases up to the planeof contour and then decreases due to the blockage of flow by theflameholder means 40) and that the flow area of the by-pass or fanpassages 27 is increasing up to plane of contour and thereafter (exceptfor an insignificant increase) decreases. The combined or total area ofboth streams, of course, increases. This arrangement, which we havetermed "shared diffusion", is effective to prevent the over-diffusionand attendant pressure loss which can occur in the conventional mixerwherein the contour of the walls is such that the actual flow area ofthe hot gas generator stream is continually increasing to the mixer exitand the fan stream area is also constant (increasing) as shown in FIG. 6(shaded areas). An additional benefit from the contoured common passagewall 26 is greater mechanical stability in the mixing device. This isimportant since a high Mach turbofan engine could suffer from severevibratory stresses were the mixer walls flst along their entire axiallength.

FIG. 7 shows a different embodiment of the three staged fuel injectionmeans of the invention. In this case, both the light-off or initialthrust augmentation fuel injection means and the radial fuel injectionmeans are placed outside the radial flameholders 40. Thus, a firstinjection means 70 is placed immediately upstream of the apex of theradial flameholder and extending inwardly to the annular space occupiedby the circumferential flameholder 42. A second fuel injection means 71is placed just upstream of the apex of the radial flameholders andalongside the first means 70. A third fuel injection means, generallyindicated at 73, placed upstream of the mixer is adapted to provideuniform fuel injection into the mixer. An outer portion 74 of the reheatfuel injection means 73 may be used to inject fuel into the fan streamin conjunction with or sequentially to the fuel injected into the gasgenerator stream through an inner portion 75. The reason for this isthat it has been learned that for by-pass ratios up to approximately1.25 all the fuel can beneficially be injected into the gas generatorstream only, for fuel system simplicity. However, for by-pass ratiosabove 1.25 it has been found advantageous to add fuel in the fan streamto improve the rate of fuel/air mixing.

FIG. 8 is a fuel schedule graph illustrating total fuel flow in poundsper hour in the three stage system disclosed in FIGS. 1 and 2. Thus,initial light-off of aug- LII mentation is indicated by the lower linewith gas generator fuel injection shown by the second line. Finally,with addition of the fuel flow from the third or uniform fuel injectionmeans, the total fu'el flow rises still further, as indicated by thethird line. The three staged fuel injection means may be operatedsequentially or selectively'as desired, except that the initialaugmentation or light-off flow from the first fuel injection means willalways be utilized.

it will be understood that other modifications of the subject inventionas would occur to those skilled in the art are intended to be includedwithin the scope of the appended claims.

We claim:

11. in an axial flow reaction engine a mixed flow augmentation systemcomprising:

a first plurality of motive fluid flow passages;

a second plurality of motive fluid flow passages, the passages of saidfirst and second pluralities having openings interspersed incircumferential alternation about the axis of the engine; and

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality upstream of theopenings thereof, wherein the plane of maximum aerodynamic flow blockageof said members is co-planar with the plane of static pressure balancingbetween the motive fluid streams of said first and second pluralities offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation system.

2. In an axial flow reaction engine a mixed flow augmentation systemcomprising:

a first plurality of contoured fluid flow passages;

a second plurality of contoured fluid flow passages,

the passages of said first and second pluralities having downstreamopenings interspersed in circumferential alternation about the axis ofan engine;

and a plurality of radially-extending flowblockage members locatedentirely within the passages of said second plurality and downstream ofa plane of contour in said second plurality of contoured fluid flowpassages wherein walls common to both of said passage pluralities areconfigured so that upstream of said plane of contour the flow area ofeach passage of both pluralities is continually increasing in adownstream direction, and downstream of said plane of contour thenominal flow area of each of said second plurality of passages increasesat a greater rate per unit length than upstream thereof and the flowarea of each of said first plurality of passages is decreasingsubstantially in direct proportion to the area change in said secondplurality so that the overall flow diffusion ratio of said mixed flowaugmentation system is reduced and the length of the pluralities offluid flow passages minimized by diffusion sharing between adjacentpassages of said first and second pluralities.

3. in a reaction engine including bypass duct means and hot gasgenerator duct means spaced within said bypass duct means, a mixed flo'waugmentation system comprising:

a first plurality of flow passages in communications with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means, the passages of said first and second pluralitieshaving downstream openings interspersed in circumferential alternationabout the engine axis;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality upstream of theopenings thereof;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein the plane ofmaximum aerodynamic flow blockage of said members is co-plsnar with theplane of static pressure balancing between the bypass and hot gasgenerator motive fluid streams of said first and second plurality offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation system.

4. In a gas turbine engine including bypass duct means and hot gasgenerator duct means spaced within said bypass duct means, a mixed flowaugmentation system comprising:

a first plurality of flow passages in communication with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein the plane ofmaximum aerodynamic flow blockage of said members is co-planar with theplane of static pressurebaiancing between the bypass and hot gasgenerator motive fluid streams of said first and second pluralities offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation stream;

and staged fuel injection means comprising:

first means for injecting fuel locally of said circumferential flowblockage member for augmentation light-off, and

second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, said first and secondfuel injection means being operable sequentially for smooth thrustmodulation over a wide range of engine operating speeds.

5. in a gas turbine engine including bypass duct means and hot gasgenerator duct means spaced within said bypass duct means, a mixed flowaugmentation system comprising:

a first plurality of flow passages in communication with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein the plane ofmaximum aerodynamic flow blockage of said members is co-planar with theplane of static pressure balancing between the bypass and hot gasgenerator motive fluid streams of said first and second pluralities offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation system;

and staged fuel injection means comprising:

first means for injecting fuel locally of said circumferential flowblockage member for augmentation light-off;

second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and

third means for injecting fuel uniformly substantially upstream of theplane of said radial flameholders in said contoured diffusion passages,said third means injecting fuel in said second plurality of contoureddiffusion passages only for engine bypass ratios of up to approximately1.25 and injecting fuel in both said second plurality and said firstplurality of passages for bypass ratios above 1.25, said first, secondand third fuel injection means being operable sequentially for smooththrust modulation over a wide range of engine operating speeds.

6. in a gas turbine engine comprising bypass duct means and hot gasgenerator duct means spaced within said bypass duct means, a mixed flowaugmentor system comprising:

a first plurality of flow passages in communication with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein said flowblockage members are located downstream of a plane of contour in saidflow passage pluralities and walls common to both of said passagepluralities are configured so that upstream of said plane of contour theflow area of each passage of both pluralities is continually increasingin a downstream direction, and downstream of said plane of contour thenominal flow area of each of said second plurality of passages increasesat a greater rate per unit length than upstream thereof and the flowarea of each of said first plurality of passages is decreasingsubstantially in direct proportion to the area change in said secondplurality so that the overall flow diffusion ratio of said mixed flowaugmentation system is reduced and the length of the pluralities offluid passages minimized by diffusion sharing between adjacent passagesof said first and second pluralities.

7. in a turbofan engine comprising bypass duct means and hot gasgenerator duct means concentric to and within said bypass duct means, amixed flow augmentation system comprising:

a first plurality of flow passages in communication with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein said flowblockage members are located downstream of a plane of contour in saidflow passage pluralities and walls common to both of said passagepluralities are configured so that upstream of said plane of contour theflow area of each passage of both pluralities is continually increasingin a downstream direction, and downstream of said plane of contour thenominal flow area of each of said second plurality of passages increasesat a greater rate per unit length than upstream thereof and the flowarea of each of said first plurality of passages is decreasingsubstantially in direct proportion to the area change in said secondplurality so that the overall flow diffusion ratio of said mixed flowaugmentation system is reduced and the length of the pluralities offluid flow passages minimized by diffusion sharing between adjacentpassages of said first and second pluralities;

and staged fuel injection means comprising:

first means for injecting fuel locally of said circumferential flowblockage member for augmentation light-off; and

second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, said first and secondfuel injection means being operable sequentially for smooth thrustmodulation over a wide range of engine operating speeds.

8. in a turbofan engine comprising bypass duct means and hot gasgenerator duet means concentric to and within said bypass duct means; amixed flow augmentation system comprising:

a first plurality of flow passages in communication with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein said flowblockage members are located downstream of a plane of contour in saidflow passage pluralities and walls common to both of said passagepluralities are configured so that upstream of said plane of contour theflow area of each passage of both pluralities is continually increasingin a downstream direction, and downstream of said plane of contour thenominal flow area of each of said second plurality of passages increasesat a greater rate per unit length than upstream thereof and the flowarea of each of said first plurality of passages is decreasingsubstantially in direct proportion to the area change in said secondplurality,

so that the overall flow difiusion ratio of said mixed 1 flowaugmentation system is reduced and the length of the pluralities offluid flow passages minimized by diffusion sharing between adjacent pas:sages of said first and second pluralities;

and staged fuel injection means comprising:

first means for injecting fuel locally of said circumferential fiowblockage member for augmentation light-off;

second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and

third means for injecting fuel uniformly substantially upstream of theplane of said radial flameholders in said second plurality of contouredfluid flow passages, said third means being adapted to inject fuel insaid second plurality of contouredfiuid flow passages only for enginebypass ratios of up to approximately 1.25 and in both said secondplurality and said first pluralies of passages for bypass ratios above1.25, said first, second and third fuel injection means being operablesequentially for smooth thrust modulation over a wide range of engineoperating speeds.

9. In a turbofan engine including bypass duct means and hot gasgenerator duct means concentric to and within said bypass duct means, amixed flow augmentation system comprising:

a first plurality of flow passages in communication with said bypassduct means;

a second plurality of flow passages in communication with said hot gasgenerator duct means, the passages of said first and second pluralitieshaving downstream openings interspersed in circumferential alternationabout the engine axis;

a plurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality upstream of theopenings thereof;

a circumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein the plane ofmaximum aerodynamic flow blockage of said members is co-planar with theplane of static pressure balancing between the bypass and hot gasgenerator motive fluid streams of said first and second pluralities offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation system; and staged fuelinjection means comprising:

first means for injecting fuel locally of said circumferential flowblockage member for augmentation light-off;

second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and

third means for injecting fuel uniformly substantially upstream of theplane of said radial flameholders in said second plurality of contouredfluid flow passages, said first, second and third fuel injection meansbeing operable sequentially for smooth thrust modulation over a widerange of engine operating speeds.

10. In a turbofan engine including bypass duct means and hot gasgenerator duct means concentric to and within said bypass duct means, amixed flow augmentation system comprising:

a first plurality of contoured fluid flow passages in flow communicationwith said bypass duct means;

a second plurality of contoured fluid flow passages in flowcommunication with said hot gas generator duct means,the passages ofsaid first and second pluralities being interspersed in circumferentialalternation about the axis of said engine, wherein walls common to bothof said passage pluralities are configured so that upstream of a planeof contour the flow area of each passage of both pluralities isincreasing in a downstream direction, and downstream of said plane ofcontour the nominal flow area of each of said second plurality ofpassages increases at a greater rate per unit length than upstreamthereof, and the flow area of each of said first plurality of passagesis decreasing substantially indirect proportion to the area change insaid second plurality;

a plurality of radially-extending flameholders located entirely withinthe passages of said second plurality, the plane of maximum aerodynamicflow blockage of said flameholders being co-planar with the plane ofstatic pressure balancing between said bypass and said hot gas generatorstreams, said flameholders being located downstream of said plane ofcontour;

a circumferential flameholder in communication with the inner ends ofsaid radial flameholders and in the path of a portion of said hot gasgenerator stream, the plane of maximum aerodynamic flow blockage of saidcircumferential flameholder being co-planar with the plane of staticpressure balancing between said first and second passage pluralities;

and staged fuel injection means comprising:

first means for injecting fuel locally of said circumferential flowblockage member for augmentation light-off;

second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and

third means for injecting fuel uniformly substantially upstream of theplane of said radial flameholders in said second plurality of contouredfluid flow passages, said first, second and third fuel injection meansbeing operable sequentially for smooth thrust modulation over a widerange of engine operating speeds.

l i f: a t

1. In an axial flow reaction engine a mixed flow augmentation systemcomprising: a first plurality of motive fluid flow passages; a secondplurality of motive fluid flow passages, the passages of said first andsecond pluralities having openings interspersed in circumferentialalternation about the axis of the engine; and a plurality ofradially-extending flow blockage members located entirely within theflow passages of said second plurality upstream of the openings thereof,wherein the plane of maximum aerodynamic flow blockage of said membersis co-planar with the plane of static pressure balancing between themotive fluid streams of said first and second pluralities of flowpassages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation system.
 2. In an axial flowreaction engine a mixed flow augmentation system comprising: a firstplurality of contoured fluid flow passages; a second plurality ofcontoured fluid flow passages, the passages of said first and secondpluralities having downstream openings interspersed in circumferentialalternation about the axis of an engine; and a plurality ofradially-extending flow blockage members located entirely within thepassages of said second plurality and downstream of a plane of contourin said second plurality of contoured fluid flow passages wherein wallscommon to both of said passage pluralities are configured so thatupstream of said plane of contour the flow area of each passage of bothpluralities is continually increasing in a downstream direction, anddownstream of said plane of contour the nominal flow area of each ofsaid second plurality of passages increases at a greater rate per unitlength than upstream thereof and the flow area of each of said firstplurality of passages is decreasing substantially in direct proportionto the area change in said second plurality so that the overall flowdiffusion ratio of said mixed flow augmentation system is reduced andthe length of the pluralities of fluid flow passages minimized bydiffusion sharing between adjacent passages of said first and secondpluralities.
 3. In a reaction engine including bypass duct means and hotgas generator duct means spaced within said bypass duct means, a mixedflow augmentation system comprising: a first plurality of flow passagesin communication with said bypass duct means; a second plurality of flowpassages in communication with said hot gas generator duct means, thepassages of said first and second pluralities having downstream openingsinterspersed in circumferential alternation about the engine axis; aplurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality upstream of theopenings thereof; a circumferentially-extending flow blockage member incommunication with the inner ends of said radially-extending members andlocated in the path of a portion of the hot gas generator stream,wherein the plane of maximum aerodynamic flow blockage of said membersis co-planar with the plane of static pressure balancing between thebypass and hot gas generator motive fluid streams of said first andsecond plurality of flow passages, respectively, to facilitate flowmixing and combustion stability in said mixed flow augmentation system.4. In a gas turbine engine including bypass duct means and hot gasgenerator duct means spaced within said bypass duct means, a mixed flowaugmentation system comprising: a first plurality of flow passages incommunication with said bypass duct Means; a second plurality of flowpassages in communication with said hot gas generator duct means; aplurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality; acircumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein the plane ofmaximum aerodynamic flow blockage of said members is co-planar with theplane of static pressure balancing between the bypass and hot gasgenerator motive fluid streams of said first and second pluralities offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation stream; and staged fuelinjection means comprising: first means for injecting fuel locally ofsaid circumferential flow blockage member for augmentation light-off,and second means for injecting fuel locally of said radial flameholdersfor intermediate power requirements of said engine, said first andsecond fuel injection means being operable sequentially for smooththrust modulation over a wide range of engine operating speeds.
 5. In agas turbine engine including bypass duct means and hot gas generatorduct means spaced within said bypass duct means, a mixed flowaugmentation system comprising: a first plurality of flow passages incommunication with said bypass duct means; a second plurality of flowpassages in communication with said hot gas generator duct means; aplurality of radially-extending flow blockage members located entirelywithin the flow passages of said second plurality; acircumferentially-extending flow blockage member in communication withthe inner ends of said radially-extending members and located in thepath of a portion of the hot gas generator stream, wherein the plane ofmaximum aerodynamic flow blockage of said members is co-planar with theplane of static pressure balancing between the bypass and hot gasgenerator motive fluid streams of said first and second pluralities offlow passages, respectively, to facilitate flow mixing and combustionstability in said mixed flow augmentation system; and staged fuelinjection means comprising: first means for injecting fuel locally ofsaid circumferential flow blockage member for augmentation light-off;second means for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and third means forinjecting fuel uniformly substantially upstream of the plane of saidradial flameholders in said contoured diffusion passages, said thirdmeans injecting fuel in said second plurality of contoured diffusionpassages only for engine bypass ratios of up to approximately 1.25 andinjecting fuel in both said second plurality and said first plurality ofpassages for bypass ratios above 1.25, said first, second and third fuelinjection means being operable sequentially for smooth thrust modulationover a wide range of engine operating speeds.
 6. In a gas turbine enginecomprising bypass duct means and hot gas generator duct means spacedwithin said bypass duct means, a mixed flow augmentor system comprising:a first plurality of flow passages in communication with said bypassduct means; a second plurality of flow passages in communication withsaid hot gas generator duct means; a plurality of radially-extendingflow blockage members located entirely within the flow passages of saidsecond plurality; a circumferentially-extending flow blockage member incommunication with the inner ends of said radially-extending members andlocated in the path of a portion of the hot gas generator stream,wherein said flow blockage members are located downstream of a plane ofcontour in said flow passage pluralities and walls common to both ofsaid passage pluralities are configured so that upstream of said planeof contour the flow area of each passage of both pluralities iscontinually increasing in a downstream direction, and downstream of saidplane of contour the nominal flow area of each of said second pluralityof passages increases at a greater rate per unit length than upstreamthereof and the flow area of each of said first plurality of passages isdecreasing substantially in direct proportion to the area change in saidsecond plurality so that the overall flow diffusion ratio of said mixedflow augmentation system is reduced and the length of the pluralities offluid passages minimized by diffusion sharing between adjacent passagesof said first and second pluralities.
 7. In a turbofan engine comprisingbypass duct means and hot gas generator duct means concentric to andwithin said bypass duct means, a mixed flow augmentation systemcomprising: a first plurality of flow passages in communication withsaid bypass duct means; a second plurality of flow passages incommunication with said hot gas generator duct means; a plurality ofradially-extending flow blockage members located entirely within theflow passages of said second plurality; a circumferentially-extendingflow blockage member in communication with the inner ends of saidradially-extending members and located in the path of a portion of thehot gas generator stream, wherein said flow blockage members are locateddownstream of a plane of contour in said flow passage pluralities andwalls common to both of said passage pluralities are configured so thatupstream of said plane of contour the flow area of each passage of bothpluralities is continually increasing in a downstream direction, anddownstream of said plane of contour the nominal flow area of each ofsaid second plurality of passages increases at a greater rate per unitlength than upstream thereof and the flow area of each of said firstplurality of passages is decreasing substantially in direct proportionto the area change in said second plurality so that the overall flowdiffusion ratio of said mixed flow augmentation system is reduced andthe length of the pluralities of fluid flow passages minimized bydiffusion sharing between adjacent passages of said first and secondpluralities; and staged fuel injection means comprising: first means forinjecting fuel locally of said circumferential flow blockage member foraugmentation light-off; and second means for injecting fuel locally ofsaid radial flameholders for intermediate power requirements of saidengine, said first and second fuel injection means being operablesequentially for smooth thrust modulation over a wide range of engineoperating speeds.
 8. In a turbofan engine comprising bypass duct meansand hot gas generator duct means concentric to and within said bypassduct means; a mixed flow augmentation system comprising: a firstplurality of flow passages in communication with said bypass duct means;a second plurality of flow passages in communication with said hot gasgenerator duct means; a plurality of radially-extending flow blockagemembers located entirely within the flow passages of said secondplurality; a circumferentially-extending flow blockage member incommunication with the inner ends of said radially-extending members andlocated in the path of a portion of the hot gas generator stream,wherein said flow blockage members are located downstream of a plane ofcontour in said flow passage pluralities and walls common to both ofsaid passage pluralities are configured so that upstream of said planeof contour the flow area of each passage of both pluralities iscontinually increasing in a downstream direction, and downstream of saidplane of contour the nominal flow area of each of said second pluralityof passages increases at a greater rate per unit length than upstreamthereof and the flow area of each of said first plurality of passages isdecreasing substantially in direct proportion to the area change in saidsecond plurality, so that the overall flow diFfusion ratio of said mixedflow augmentation system is reduced and the length of the pluralities offluid flow passages minimized by diffusion sharing between adjacentpassages of said first and second pluralities; and staged fuel injectionmeans comprising: first means for injecting fuel locally of saidcircumferential flow blockage member for augmentation light-off; secondmeans for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and third means forinjecting fuel uniformly substantially upstream of the plane of saidradial flameholders in said second plurality of contoured fluid flowpassages, said third means being adapted to inject fuel in said secondplurality of contouredfluid flow passages only for engine bypass ratiosof up to approximately 1.25 and in both said second plurality and saidfirst pluralies of passages for bypass ratios above 1.25, said first,second and third fuel injection means being operable sequentially forsmooth thrust modulation over a wide range of engine operating speeds.9. In a turbofan engine including bypass duct means and hot gasgenerator duct means concentric to and within said bypass duct means, amixed flow augmentation system comprising: a first plurality of flowpassages in communication with said bypass duct means; a secondplurality of flow passages in communication with said hot gas generatorduct means, the passages of said first and second pluralities havingdownstream openings interspersed in circumferential alternation aboutthe engine axis; a plurality of radially-extending flow blockage memberslocated entirely within the flow passages of said second pluralityupstream of the openings thereof; a circumferentially-extending flowblockage member in communication with the inner ends of saidradially-extending members and located in the path of a portion of thehot gas generator stream, wherein the plane of maximum aerodynamic flowblockage of said members is co-planar with the plane of static pressurebalancing between the bypass and hot gas generator motive fluid streamsof said first and second pluralities of flow passages, respectively, tofacilitate flow mixing and combustion stability in said mixed flowaugmentation system; and staged fuel injection means comprising: firstmeans for injecting fuel locally of said circumferential flow blockagemember for augmentation light-off; second means for injecting fuellocally of said radial flameholders for intermediate power requirementsof said engine, and third means for injecting fuel uniformlysubstantially upstream of the plane of said radial flameholders in saidsecond plurality of contoured fluid flow passages, said first, secondand third fuel injection means being operable sequentially for smooththrust modulation over a wide range of engine operating speeds.
 10. In aturbofan engine including bypass duct means and hot gas generator ductmeans concentric to and within said bypass duct means, a mixed flowaugmentation system comprising: a first plurality of contoured fluidflow passages in flow communication with said bypass duct means; asecond plurality of contoured fluid flow passages in flow communicationwith said hot gas generator duct means,the passages of said first andsecond pluralities being interspersed in circumferential alternationabout the axis of said engine, wherein walls common to both of saidpassage pluralities are configured so that upstream of a plane ofcontour the flow area of each passage of both pluralities is increasingin a downstream direction, and downstream of said plane of contour thenominal flow area of each of said second plurality of passages increasesat a greater rate per unit length than upstream thereof, and the flowarea of each of said first plurality of passages is decreasingsubstantially in direct proportion to the area change in said secondplurality; a plurality of radially-extenDing flameholders locatedentirely within the passages of said second plurality, the plane ofmaximum aerodynamic flow blockage of said flameholders being co-planarwith the plane of static pressure balancing between said bypass and saidhot gas generator streams, said flameholders being located downstream ofsaid plane of contour; a circumferential flameholder in communicationwith the inner ends of said radial flameholders and in the path of aportion of said hot gas generator stream, the plane of maximumaerodynamic flow blockage of said circumferential flameholder beingco-planar with the plane of static pressure balancing between said firstand second passage pluralities; and staged fuel injection meanscomprising: first means for injecting fuel locally of saidcircumferential flow blockage member for augmentation light-off; secondmeans for injecting fuel locally of said radial flameholders forintermediate power requirements of said engine, and third means forinjecting fuel uniformly substantially upstream of the plane of saidradial flameholders in said second plurality of contoured fluid flowpassages, said first, second and third fuel injection means beingoperable sequentially for smooth thrust modulation over a wide range ofengine operating speeds.